The Lunt LS35THaDX 35mm solar refractor and accessory package puts serious Hydrogen-alpha solar viewing within the reach of virtually every astronomer. You can piggyback this lightweight (3 pound) solar scope on a larger existing telescope or mount it on a photo tripod or altazimuth mount to use as a quick grab and go scope for spur-of-the-moment observing at lunchtime or when on vacation. Because this Lunt scope is small and compact (only 16.35” long and 62mm in diameter at its widest), the LS35THaDX is ideally suited to being mounted in pairs side by side for binocular viewing.
The H-alpha filter in the Lunt 35mm Deluxe solar refractor shows you much more of the living Sun than ordinary glass or Mylar white light solar filters that only show you sunspots. With the economical Lunt LS35THaDX Deluxe package, you see the violent ever-changing tapestry of multiple prominences leaping off the edges of the solar disk, as well as sunspots and some surface detail.
The Lunt LS35THaDX is based on a fully multicoated 400mm focal length achromatic refractor with a 35mm clear aperture and an f/11.4 focal ratio. Its built-in Hydrogen-alpha solar filter is centered on the 6562.8 Ångstrom H-alpha solar emission line. The filter has a narrow <0.75 Ångstrom passband for high contrast. The two-part filter uses a permanently mounted 35mm etalon behind the objective, with a 6mm blocking filter built into the standard equipment 1.25” star diagonal.
A tuning mechanism built into the system lets you tilt the etalon to center the passband precisely on the H-alpha line for maximum contrast. The tuning mechanism also lets you perform off-band observations of Doppler-shifted disk features to determine whether they are moving towards you or away from you.
The 6mm clear aperture of the H-alpha blocking filter in the star diagonal is matched to the focal length of the telescope for both visual observing and solar imaging. It gives you a full disk image of the Sun at prime focus with almost any 1.25” eyepiece you might care to use. The diagonal’s 1.25” eyepiece holder has a built-in helical focuser that makes focusing easy, even if you are observing in the dead of winter while wearing gloves or mittens. Simply rotate the eyepiece to focus it sharply on the solar image.
The LS35T Deluxe package comes with a 10mm 1.25” Lunt Solar eyepiece. This eyepiece has a wide 70° apparent field of view, giving you a magnification of 40x and a 1.75° actual field. This gives you plenty of dark sky background around the solar disk to show off the prominences. In addition, you can use virtually any other 1.25” eyepiece you might have with this 35mm Lunt solar refractor. A typical 20mm 1.25” Plössl will give you a magnification of 20x and a little over a 2.5° field of view compared with the 0.5° diameter disk of the Sun. A 6mm Plössl will give you 67x magnification and about a 0.77° field, letting you get up close to the Sun, although the resulting very narrow 0.52mm exit pupil may start dimming the prominence detail more than you might like to see.
To make lining up on the Sun easier and safer, a TeleVue Sol-Searcher non-magnifying pinhole finder is mounted on the LS35T optical tube. The Sol-Searcher has two small circular plates spaced 2” apart. A hole in its front plate projects an image of the Sun onto a circular white panel on the back plate. To use the Sol-Searcher, simply stand off to one side of your scope with your back to the Sun. While observing the position of the Sun’s image on the Sol-Searcher’s back plate, adjust the position of your LS35T until the Sun’s image falls on the circular white panel on the back plate. Once it does, your LS35T is pointing at the Sun. It’s that simple.
In addition to the Sol-Searcher finder, the Lunt LS35THaDX package comes with mounting rings that have collimation screws so you can precisely line up the scope with the optical axis of any larger scope on which it might be piggybacked. The rings are attached to a Vixen-style dovetail with 1/4”-20 thread holes that will let you mount the scope directly on a photo tripod for a quick peek at the Sun.
You can also mount the scope’s dovetail directly onto any altazimuth or German equatorial mount that accepts a Vixen-style dovetail for easier extended observing and tracking of the Sun.
Most solar telescopes exhibit a “sweet spot” in their field of view where subtle prominences pop into clearer view and the larger prominences show more contrast and detail. Experimentally moving the Lunt LS35T/Ha Deluxe around so that the Sun’s limb and prominences move to different parts of the field will soon reveal where your particular scope’s “sweet spot” is located.